The present invention relates to novel dual-emitting lumiphores, use of same in sensors, and methods for detecting dioxygen using the sensors.
Oxygen is a critical element to many chemical processes on earth, including life itself. The capability of measuring the presence and concentration of oxygen is important to many fields of human endeavor.
Oxygen is generally found in the form of dioxygen, and this is the form in which it is generally measured. Dioxygen is an important analyte in human physiology, a commodity in the field of medicine, a measure of the health of the environment, and a necessary reagent in many industries. For the last three decades, dioxygen has been monitored with electrochemical sensors. Electrochemical sensors allow continuous monitoring of dioxygen. However, for a growing number of applications, electrochemical sensors have proven to be an unsatisfactory method of dioxygen measurement. This is because electrochemical sensors are prone to chemical and electrical interference; they consume dioxygen; and their bulk precludes miniaturization.
Optical sensors for dioxygen have overcome many of these problems found with electrochemical sensors. Importantly, they are also inexpensive and disposable. This allows greater flexibility of usage. For example, it is possible to couple optical sensors to the distal end of an optical fiber. Such systems offer remote, non-perturbing, multi-analyte analysis that can be used in a small, confined space, such as a blood vessel. (Wolfbeis, O. S.; Weis, L. J.; Leiner, M. J. P.; Zielgler, W. E. Anal. chem. 1988, 60, 2028-30 Fiber-Optic Fluorosensor for Oxygen and Carbon Dioxide.; Peterson, J. I.; Fitzgerald, R. V.; Buckhold, D. K. Anal. Chem. 1984, 56, 62-7 Fiber-Optic Probe for in Vivo Measurement of Oxygen Partial Pressure.; Xu, W.; McDonough, R. C.; Langsdorf, B.; Demas, J. N.; DeGraff, B. A. Anal. chem. 1994, 66, 4133-41 Oxygen Sensors based on luminescence Quenching: Interactions of Metal Complexes with the Polymer supports.; Lakowicz, J. R. Topics In Fluorescence Spectroscopy; Plenum Press: New York, 1994; Vol. 4.)
Most dioxygen optical sensors, including the sensor of the present invention, are based on a change in luminescence intensity emanating from a probe whose luminescence is quenched by molecular oxygen. The luminescent-probe molecules are usually encapsulated into a gas-permeable, ion-impermeable material. (Demas, J. N.; DeGraff, B. A.; Xu, W. Anal. Chem. 1995, 67, 1377-80 Modeling of Luminescence Quenching-Based Sensors: comparison of Multisite and Nonlinear Gas Solubility Models.; Mills, A.; Thomas, M. Analyst 1997, 122, 63-8 Fluoresecence-based Thin Plastic film Ion-pair Sensors for Oxygen.; Mills, A.; Thomas, M. D. Analyst 1998, 123, 1135-40 Effect of Plasticizer viscosity on the sensitivity of an [Ru(bpy)32+(ph4Bxe2x88x92)2]-based optical oxygen sensor.; Mills, A. Biosensors and Bioelectronics 1998, 51, 60-8 Controlling the sensitivity of optical oxygen sensors.; Papkovsky, D. B.; Ponomarev, G. V.; Trettnak, W.; O""Leary, P. Anal. Chem. 1995, 67, 4112-7 Phosphorescent Complexes of Porphyrin Ketones: Optical Properties and Application to Oxygen Sensing.)
Most luminescent dioxygen sensing materials (for instance polymer films) rely on quenching of the emission from a polymer immobilized ruthenium(II) diamine complex or group VIII metalloporphyrins. While these materials have demonstrated the convenience of using luminescence quenching to measure dioxygen, they have many shortcomings. For example, currently available sensor molecules have a single, long-lived emission that is quenched by molecular oxygen. When fluorescence or phosphorescence intensity is used to measure oxygen quenching, such events as photo-bleaching, changes in optical clarity, and variations in the positioning of the film relative to the source and detector may interfere with accurate measurement. These must be minimized for accurate measurement. In addition, current optical sensors are not self-correcting for variations in intensity and, therefore, the sensor must be continually restandardized. (Bacon, J. R.; Demas, J. N. Anal. chem. 1987, 59, 2780-5 Determination of Oxygen Concentrations by Luminescence Quenching of a Polymer-Immobilized Transition-Metal Complex.; Carraway, E. R.; Demas, J. N.; DeGraff, B. A.; Bacon, J. R. Anal. Chem. 1991, 63, 337-342 Photophysics and Photochemistry of Oxygen Sensors Based on Luminescent Transition-Metal Complexes)
There have been extensive efforts to improve the reliability of these systems and to limit the need for restandardization, which have led to the measurement of excited state lifetimes. These lifetimes are commonly measured using frequency-modulated excitation and a phase-sensitive lock-in amplifier. As with intensity, the excited state lifetime of the emitter decreases upon exposure to molecular oxygen. This method is amenable for use with many emission molecules, including those described by the present invention. While measuring the phase change represents an effective method for dioxygen measurement, it requires a substantial complexity in the measuring device. This increase in complexity results in increased cost and decreased reliability. (Lakowicz, J. R. Topics In Fluorescence Spectroscopy; Plenum Press: New York, 1994; Vol. 4.; Hartmann, P.; Leiner, M. P. J.; Kohlbacher, P. Biosensors and Bioelectronics 1998, 51, 196-202 Photobleaching of a ruthenium complex in polymers used for oxygen optodes and its inhibition by singlet oxygen quenchers.; Thompson, R. B.; Lakowicz, J. R. Anal. Chem. 1993, 65, 853-856 Fiber OPtic sensor based on phase fluorescence lifetimes.; Wolfbeis, O. S.; Klimant, I.; Werner, T.; Huber, C.; Kosch, U.; Krause, C.; Neurauter, G.; Durkop, A. Biosensors and Bioelectronics 1998, 51, 17-24 Set of Luminescence decay time based chemical sensors for clinical applications.; Ogurtsov, V. I.; Papkovsky, D. B. Biosensors and Bioelectronics 1998, 51, 377-81 Selection of modulation frequency of excitation for luminescence lifetime-based oxygen; Multimetallic and Macromolecular Inorganic Photochemistry in the Series Molecular and Supramolecular Photochemistry; The Photophysics and Photochemistry of 1,2-enedithiolates Pilato, R. S. (Schanze, K.; Ramamurthy, V. ed.) 1999 vol. 4, Chpt. 5. pages 185-214 Marcel Dekker Inc., New York)
The present invention describes new dioxygen sensors based upon dual-emitting luminescent platinum 1,2-enedithiolates. By the nature of the dual emission, these sensors are more accurate, more reliable, and more versatile than those sensors considered current art.
The discovery of the dual-emitting complexes described eliminates the need for continual restandardization of the sensor and the need to use frequency modulation to measure dioxygen. In addition, these dual-emitting sensors can be easily adapted for use as simple inserts in common fluorescence cuvetts, which further expands their application.